Rear seats in some vehicle may be equipped with a device to adjust a reclining angle and a seat height to improve user experience. For a rear seat with a reclining mechanism, a gap between a rear seat and a package tray of a rear window must be provided so that the rear seat can move relative to the package tray. A cover plate is commonly used to conceal the gap. For example, in the vehicle shown in FIG. 1, an end of a cover plate 1 is connected to a rear side of a rear seat 2, and another end of the cover 1 is connected to a package tray 3. However, if the cover plate 1 is fixed to the rear side of the rear seat 2, a height of the connection point relative to a vehicle floor will change when the rear seat reclines, which results in an inclination of the cover plate 1 and thus creates a gap between the cover plate 1 and the package tray 3. When an object falls into the gap, it is difficult for a user to dissemble the cover plate to retrieve the fallen object. If the cover plate 1 is slidably connected to the rear side of the rear seat 2, a rail or a connecting part may be exposed during movement of the rear seat, which affects the appearance. Thus, there is need for a gap cover assembly which provides detachable connection with a rear seat.